But would they have done this without Mozilla pushing the performance with asm.js, or that fast? Competition is great, and it also makes me wonder, if they keep this up - maybe NaCl won't be needed either?
edit: Video link http://www.youtube.com/watch?v=IXIkTrq3Rgg
JavaScript is not some immutable thing. It needs enhancing, not replacing.
I looked at the spec briefly (http://wiki.ecmascript.org/doku.php?id=strawman:value_object...), but it doesn't talk about the how.
I understand nan-boxing and similar techniques, but they seem to imply at least some runtime overhead to test the type of the value in some cases. Also, AFAIK, 64 bit integers cannot be represented with nan-boxing, as there are only 51 bits available for the payload.
On the other hand, Dart doesn't have required type annotations either and it has 64-bit ints, doesn't it? So it should be possible to introduce in JS.
Runtime overhead is likely, but then when you're in the JIT sweet spot the types are all known so you get JITcode that doesn't check types.
GC is a related example of a place where VM designers told us not to worry ourselves, but it turns out that GC is inherently hard and you are going to pay for that convenience - either in performance or in memory. See: http://sealedabstract.com/rants/why-mobile-web-apps-are-slow....
I agree that not having to rely on the JIT to figure out how to optimize your code with 'magic' is preferable. I tend to lean towards that where possible in most of the JIT/GC-based environments I use (C#, JavaScript, etc), and it tends to pay off.
This is precisely what "use asm" is for. It gives you direct control: each allowable operation in the subset has a direct analogue to the appropriate machine instruction(s). If you fall off the happy path and stray into "JIT magic" territory, you get a message in the developer console telling you to fix your code.
Unfortunately V8 is opposed to "use asm" in favor of the "JIT magic".
There are already multiple types in JavaScript, and this already affects performance; for example "+" is defined for both numbers and strings. All JavaScript engines handle this in the same way, more or less. You start out with a "baseline JIT" that does not make assumptions about the types of objects and has type-check-and-dispatch on operations like "+". These type checks record the types of objects that have flowed through each point. Once enough types have flowed through so that we can reasonably predict the types, we recompile the function to assume that the same type (for example, number) goes through, which enables greater optimizations. You then hoist type guards up (or eliminate them if you can prove them never taken) so that you deoptimize and bail out.
Value objects don't change this overall picture, they just add more types.
All of this, however, is irrelevant to asm.js. With an ahead-of-time optimizing compiler, we know what the types are beforehand via the asm.js spec. So there are no type guards inserted at all, and none of this is an issue. For example, NaN-boxing is not used in the Firefox asm.js compiler (OdinMonkey). We know which values are doubles and which are integers, so we need no runtime guards or type tests at all.
The target for most of this is porting C games to the Web, and many modern C games use all kinds of multithreading and blocking I/O. Game programmers are not interested in safety, they are interested in performance.
Yes, message passing leads to fewer bugs. It also leaves a lot of performance on the table if you are trying to maximize usage of CPU resources on an SMP architecture.
The funny thing here is that gave devs are still kind of weary of threading bugs, and blocking I/O was something that was probably earliest dealt with by the people having to stream content off of spinning plastic discs.
A VM or high level compiler abstraction, especially with GC, tends to interfere with #1, and sandboxed environments with abstract APIs for accessing hardware tend to interfere with #2.
Yes, this is not to say that games won't use scripting, like Lua or UnrealScript, but those are not part of the rendering loop.
Asm.js provides predictability in terms of GC, but it does not ensure predictability in terms of performance (because of differing JIT implementations), nor does it give the direct access to hardware resources one would like (e.g. SMP).
I don't really see it as a target for next-gen games, regardless of the cool UnrealEngine demos. Mobile casual games maybe.
For #1, asm.js doesn't have GC, by and large (there are a couple of places where the GC gets used when interacting with Web APIs, but those are fixable and don't matter much in practice). For #2, "a sandboxed environment with abstract APIs for accessing hardware" precisely describes Pepper!
> Asm.js provides predictability in terms of GC, but it does not ensure predictability in terms of performance (because of differing JIT implementations), nor does it give the direct access to hardware resources one would like (e.g. SMP).
I don't understand what you mean. The performance predictability is fixed by "use asm" and AOT compilation. V8 is opposed, but your point (rightly, IMHO!) argues against that choice. If you're just arguing that there will be multiple implementations of asm.js and that's bad for predictability I don't see that being fixed with any solution outside of a browser monopoly. If PNaCl is to become a cross-browser solution, then you must be open to alternative implementations.
As for threads, we can continue to evolve JavaScript so that it is supported, at least in asm.js mode. I don't see this as some fundamental obstacle.
Yes, pepper is an abstraction, but you get concurrency primitives which is lower level than asm.js.
The reality is, neither asm.js nor NaCl are going to succeed in getting the gamedev community onto the web platform. The two most popular platforms, iOS and Android, have native SDKs, and so do the consoles and desktops, so any developer who wants to maximize revenue is going to want to target those. The additional headache of a browser port onto a heavily fragmented platform with unpredictable performance, and an audience that has shown little appetite for paying for web apps pretty much guarantee that this whole asm.js vs NaCL debate is moot.
Developers just don't care about runtime portability as far as games are concerned. They will do the work to do a source port for optimal performance if the market is there.
Does Electronic Arts or Valve care about getting Battlefield 4 or Portal 2 running in the browser in a portable way? I highly doubt it.
The PS3 SPUs also didn't have access to system memory, and SPU code had to be compiled into small "executables", so in a twisted way this is a similar model to WebWorkers ;)
Shared TypedArrays would be nice, but only if this also comes with a complete set of atomic operations. But in my opinion, vector datatypes would be more important in the short term for JS (so it can make use of SSE under the hood).
Which is already more than proven that only leads to threading bugs.
I agree that we don't want to break the single-threaded JS model. But we have options, the easiest of which is to restrict shared mutable state to ArrayBuffers and asm.js, or asm.js-like code.
In this cas mozilla is the one that took the lead on the asm.js case, and healthy competition is always better, but I believe it makes no doubt that the v8 team would have worked at improving their js speed as much as possible even without that pinch from mozilla.
That's not accurate. I recommend you go back and look at the actual order of events here.
Apple started the JS perf battle with SquirrelFish Extreme and Firefox answered with TraceMonkey, all before Chrome was even announced.
I am not discounting the impact that V8 has had on the industry, but it is simply wrong to claim that Google kicked this thing off when Apple and Mozilla were both there publicly squaring off in JS benchmarks well before you, and just about every one else on the planet, even knew Chrome was a thing.
http://nontroppo.org/timer/kestrel_tests/
and when Safari was still an early beta Opera was marketed as "The Fastest Browser on Earth".